In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An ink jet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-recording layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support. Medical images, such as radiographic images, are typically viewed on a blue transparent support.
While a wide variety of different types of image-recording elements for use with ink jet devices have been proposed heretofore, there are many unsolved problems in the art and many deficiencies in the known products which have severely limited their commercial usefulness. The requirements for an image recording medium or element for ink jet recording are very demanding.
It is well known that in order to achieve and maintain photographic-quality images on such an image-recording element, an ink jet recording element must:
Be readily wetted so there is no puddling, i.e., coalescence of adjacent ink dots, which leads to nonuniform density PA1 Exhibit no image bleeding PA1 Provide maximum printed optical densities PA1 Exhibit the ability to absorb high concentrations of ink and dry quickly to avoid elements blocking together when stacked against subsequent prints or other surfaces PA1 Provide a high level of gloss and avoid differential gloss PA1 Exhibit no discontinuities or defects due to interactions between the support and/or layer(s), such as cracking, repellencies, comb lines and the like PA1 Not allow unabsorbed dyes to aggregate at the free surface causing dye crystallization, which results in bloom or bronzing effects in the imaged areas PA1 Have an optimized image fastness to avoid fade from contact with water or radiation by daylight, tungsten light, or fluorescent light PA1 Provide image stability under high-humidity conditions PA1 a) providing an ink jet recording element as described above, and PA1 b) applying liquid ink droplets thereon in an image-wise manner.
Image stability is an important concern for inkjet prints. In particular, dyes used in the printing process may continue to migrate over time during storage of a printed image. The migration process typically occurs more quickly under conditions of high relative humidity since inkjet dyes are water soluble and materials used to manufacture inkjet media are often easily plasticized by water. Within a given dye set, the individual dyes may migrate or bleed at different rates due to differences in solubility or molecular dimensions. As a result, areas which are originally printed as neutral densities may acquire a colored tint over time. Such a phenomenon is especially objectionable in a medical application such as a radiographic image, since a neutral gray scale is expected and a colored tint is typically unacceptable in any area of the print.
U.S. Pat. No. 4,547,405 relates to an ink jet receiver comprising an ink jet recording layer which contains a polymeric latex of a block copolymer of polyvinyl alcohol and polyvinyl (benzyl ammonium chloride). However, there is a problem with this material in that, under high humidity conditions, the image stability is not as good as one would like.
Other prior art references such as U.S. Pat. No. 5,916,673 discloses that trivalent salts or ions of Group IIIb metals may be added to ink jet recording sheets for the purpose of improving waterfastness of images without compromising lightfastness. However, it has been found that such salts or ions of metals in reality actually contribute to poorer color stability under high humidity conditions.
It is an object of this invention to provide an ink jet receiver in which the color does not shift under high humidity conditions.